I have a 2G 2018 and it has a dipstick. In the engine compartment, look in the front right - and look deep down. There is a dipstick.You mean "have the fluid level checked". Honda doesn't provide owners with instructions on how to check or replace the transmission fluid in the 2G Ridgeline.
From the Owner's Manual:
"Have a dealer check the fluid level and replace if necessary.
Do not attempt to check or change the automatic transmission fluid yourself."
The transmission should still be covered under the balance of the 5/60 powertrain warranty regardless of where the vehicle was purchased.
If it was purchased from a Honda dealer and the dealer sold it as Honda Certified Pre-Owned, then it should be covered for 7/100.