Update a document type constant

I don't think updating the type of a constant is possible. Neither from the OOTB smart services nor using any plugin as of today. 

but Update Constant smart service is available in Process model 

That is only to update the value. Not the type. 

Here is the documentation - https://docs.appian.com/suite/help/22.2/Update_Constant_Smart_Service.html#:~:text=The%20Update%20Constant%20Smart%20Service,constant%20with%20the%20new%20value.


If you are trying to update the value of a constant, it should work fine, provided you have appropriate rights. Check the documentation for more. 

Did you see any error messages? Has your user the right permissions?

oops I have a constant of a document type , in that constant I have to change the value w.r.t to new document which has been published latest .

Just edited the above comment and added a documentation link. It includes some of the scenarios in which the service will not work. 

No I am not getting any error . but value is getting blank or [NotVisible] in the constant 

Can you post a screenshot of your node setup?

Try removing the value from "Save Into" and re-try.