I just filed my 2019 taxes, I have to mail it in. Should I mail the tax owed along with the return?

[NCperson]

YES - that will cut off the penalties and interest for late payment. 

[VolvoGirl]

Or you can pay it directly online.  Pay the IRS directly at

Https://www.irs.gov/payments

[xmasbaby0]

And just so you know.......paying the tax due as shown on the return will not be the end.   Your penalties and interest have been adding up since the filing deadline for that return, so you can expect a bill from the IRS for that someday, but it may take a few months.