I want only users with admin role to see a button in jira.
I want to find scriptrunner code where I can provide this restriction.
You shouldn't need to do anything fancy with scriptrunner to do this. All you need to do is set a condition on the transition you wish to only expose to a limited group or role.
Ex: Condition = Only users in group Admin can perform this transition
Condition = Only users in Project Role Admin can perform this transition