CSV string

You can use split() function which splits text into a list of text elements, delimited by the text specified in the separator. In your case delimiter is ",". 

https://docs.appian.com/suite/help/21.3/fnc_text_split.html

split("ABC,ABC,2,06:00:00,18:00:00,0.5,3
XYZ,XYZ,3,06:00:00,18:00:00,0.5,3", ",")

This will return individual elements from your original string that are separated by comma. You can then use a!foreach() to iterate over each element.

i have many lines, in each line it is seperated by comma's

First, use split to get the lines using "char(10)" as the delimiter. Then, in a foreach, use the comma delimiter to get the values for each line.

I have string called "abc:3" ,"xyz:4" , i want update yyy column "xyz:5"  it should update in database through process model, how to do.

fyi:-

This tutorial would be a good start

docs.appian.com/.../Records_Tutorial.html

I can do by related actions from  record.. but i have value from string 

I would create a CDT matching the target data model. Then create an expression which turns the string into a list of that CDT. Then show it to the user for editing and store it to DB later.

Yes, first split lines by newline, then split each line moto x3m by commas.