Sorry you will have to start fresh with 2 returns. Don't try to copy or transfer your Joint return into a Single returns. You can not remove the primary spouse listed or change the spouse to be primary.
Removing a spouse is not recommended
https://ttlc.intuit.com/community/family/help/how-do-i-remove-a-former-spouse-from-my-return/00/2720...
Here's some other links. They might be old I haven't checked them yet.
Getting Divorced article
https://turbotax.intuit.com/tax-tips/marriage/getting-divorced/L20NC66cf
Video tips for Divorced couples
https://turbotax.intuit.com/tax-tips/marriage/video-tax-tips-for-divorced-couples/L8YqvF7p5
And see what AGI to use
https://ttlc.intuit.com/community/agi/help/what-agi-should-i-enter-if-i-m-recently-divorced-or-widow...
