Hiya Hiten,
If everyone'e previous SKU is the same, then this won't be an issue - it'll be a simple case of:
or
gam all users update license 1010020027 from Google-Apps-For-Business
I believe the SKU's you're looking for are:
1010020027 - Google Workspace Business Starter license
Google-Apps-For-Business - GSuite Basic license
The problem you face is that when it comes to changing a license, you have to specify the old SKU. If they have a bunch of different licenses, I would suggest making a CSV file of the old SKU's and reference like so:
gam csv c:\choose\your\path.csv gam all users update license 1010020027 from ~[put csv header here]
More info:
Thanks,
Zack