Schedule E?  Huh?

If the vehicle is being used for his Schedule C business, no, you can't claim it is being used for rental property on Schedule E.  Why would you think that would be allowed?

The truck is used about 95% for his rentals properties, the Sch c income is actually from related business he owns but have treir own seperate returns

Schedule C income is from other business he owns and gets a payment from, the truck is actually 95% for current business

What???  One post you just said it is used 95% for the rentals, and a minute later you said it was used 95% for the business.  You need to get things straight.

At any rate, the deduction goes with the activity and on the Schedule that the vehicle was used for, and that could even be both.  If it was used for Schedule E rentals, those miles go on Schedule E.  If it was used for the Schedule C business, those miles go on Schedule C.

If 2019 was wrong, that should be amended.

"...the Sch c income is actually from related business he owns but have treir own seperate returns"

That comment is so wrong I'm not sure where to start.

If that related business he "owns" files "trier own seperate returns" (sic) - then it isn't a Sch C.   A Sch C has ONE owner (unless married in a community property state).

"The truck is used about 95% for his rentals properties,"

Then the way it was first reported was, "Let's pick our own adventure and see if anyone notices?" And we thought we were maximizing the tax rules to our benefit, but a year later, we see why it pays to do it right.

This would be a good time to amend, then.