How do I get a RAPID variable from RAPID through a web service and write a new value

Help me. Thank you.

Hi, Here is a tutorial in REST: https://www.drdobbs.com/web-development/restful-web-services-a-tutorial/240169069 (Although a lot of great resources exists)

For writing to the robot with ABB robot web services, check out the following:
Update RAPID Variable Current/Init Value: /rw/rapid/symbol/{symbolurl}/data
Link: ABB-Robot Web Services

You could also use DIPC for this: /rw/dipc/{queue-name}
Link: ABB-Robot Web Services