jira scriptrunner How to set form value for select( single choice)

[Qi Jiang]

I created 3 custom field(A,B,C) under issue. They are all single choice. 

Options:

A: 1, 2, 3

B: a, b, c

C: i, ii, iii

Goal, Once custom field A value set to 1, custom B,C will auto filled to a and i.

[Joshua Yamdogo @ Adaptavist]

Let's continue discussion here:

https://community.atlassian.com/t5/Atlassian-Marketplace-questions/jira-scriptrunner-set-form-value-for-select-single-choice/qaq-p/621402

[Tarun Sapra]

Scenarios like these have been discussed many times on this forum.

Possible duplicate - https://community.atlassian.com/t5/Atlassian-Marketplace-questions/script-runner-set-value-in-a-select-list-field/qaq-p/101245 

[Qi Jiang]

Hi Tarun, where should I post? Could you show me steps where to post these code?