Do you know the amount?  Just enter it as Other self employment income or as Cash or General income.  You don't need to get a 1099NEC or 1099K.  Even if you did you can enter all your income as Cash.  Only the total goes to schedule C.

How to enter income from Self Employment

https://ttlc.intuit.com/community/self-employed/help/how-do-i-report-income-from-self-employment/00/...

Agreed ... skip the idiot and simply report all your income on the Sch C and just skip the 1099 entry section ...

The fact that he has failed to issue 1099 forms is HIS problem when he is audited  not yours if you simply report all your income on your Sch C and this will CYA.

I thank you both from the bottom of my heart. I was finally able to finish my taxes today.