Process model

you can not come back to process start form. You can create a seperate user input task for the same form which you used into start event. From the second user input task, you can set the value to these button and pass it to process variable and check the variable value via XOR gateway and set the flow accordingly.

No I cannot able to create the user input task becoz this process model is used in site and a site must have a process start form

One question, on click of cancel you want to end the process instance and start a new one or you want to stay on the same instance? if you want to stay on the same instance then there will be a start form and user input tasks with the same interface(1st UIT with interface1 and 2nd UIT with interface2 and process start form with interface1). both should be there for the process start form interface. After the cancel click, you will go towards the user input task1 which is having the same interface as process start form.

One question, on click of cancel you want to end the process instance and start a new one or you want to stay on the same instance? if you want to stay on the same instance then there will be a start form and user input tasks with the same interface(1st UIT with interface1 and 2nd UIT with interface2 and process start form with interface1). both should be there for the process start form interface. After the cancel click, you will go towards the user input task1 which is having the same interface as process start form.

I want to stay on the same instance

Then you can follow the below approach.

The first thing OP mentioned was that he is using this process as a landing page on a site. 

Here is a reference for you - docs.appian.com/.../Sites.html

Harshit, If you know we can use process model with start form into the site as well. so if you see the picture i mentioned start event with interface1 which mean OP has to give interface 1 in the start form and OP also mentioned they move to second interface which is not into interface 1. i.e he is using UIT for that and now on click on the cancel button he want to go the start form which is not possible but want to stay on the same instance which means we have to use another UIT. Please correct if i am wrong somewhere.

For more i am quoting his query below:

Unknown said:

that is outside of the landing page interface

Unknown said:

In that Interface 2 there is cancel button  when I hit that it want to come back to the interface 1 in the landing page

Unknown said:

I want to stay on the same instance

Moreover, if he want to complete the successive form in the single sitting then he can use the Activity chaining as well between all the nodes(UIT).

You can ONLY use a process with a start form. There is a difference. 
Also, f you are asking the OP to map interface 1 in the start node then how do you plan to connect interface 2 with 1?

To go to interface 2 from the interface 1(start form) there is a button which will submit the form and take the flow to form 2.

Unknown said:

I am having a interface(interface 1) inside that after I hitting the submit button it is going to display and another interface(interface 2)

Read my question again. I am asking about going from 2 to 1 in the same instance with a  start form. 

you can read OP's question again and if required have a look on the image as well which i attached. on click on cancel button in Interface 2 we are using XOR gateway to check the condition. if submit button click then the flow will end else it will go to user input task(interface1).

Please see the UIT labels as well.

Humble request to have a look on below.

You can label the interface any number but that doesn't solves the actual problem here. Anyway, udhayakumarm0001, going back to same interface is possible but not in the same instance, when you have this process plugged as a site page.
You can just end the process when cancel button is pressed on interface 2 and that should take you back to interface 1. 

Thanks Deepak gupta It is worked