Hello,
Thank you for contacting the support and sorry for any inconvenience that might have been caused due to that.
You don’t need to remove the old sitemap from GSC Google will automatically fetch the new sitemap since it’s already inside your main (sitemap_index.xml) file.
Hope that helps and please do not hesitate to let us know if you need our assistance with anything else.
Hello,
Since we did not hear back from you for 15 days, we are assuming that you found the solution. We are closing this support ticket.
If you still need assistance or any other help, please feel free to open a new support ticket, and we will be more than happy to assist.
Thank you.