@Aruna10 Instead of assigning the role to individual users, create a group add those 1000 users in that group and assign the role to the group.
As a first step, you need to
1. Create a group
2. Add impersonate role to the group
3. Add user's to the group
First two steps are simple, for the third one you can write a fix script to add those thousand users into the group list. You can either read the list from an excel or CSV find the matching records based on the first name and last name from the sys_user table and add the reference in sys_user_grmember table.
Hope this helps.
