Second mortgage on investment property to capitalize equity

[Balo Mutho]

For primary homes, one can do HELOC or cash out refi.

For an investment home, what is the best way to take out a second mortgage, while a first mortgage is still in place?

Are there speciality investors, or are there any suggestions?

I have a 792 credit score, if that helps, with rental property being rented for 4 + years.