Close both tanks, make sure that the system items are all off, stove, grill, etc. disconnect both lines then reconnect them. Once reconnected slowly open the valve on the tank the valve is towards. Once on turn the other tank on. Then, go check the stove. Hopefully you have gas flowing.
LPG valves have a safety built in, if the system is at zero when you turn the vales on the tank thinks there's a leak and shuts down.
Hope this helps and welcome!
Now-2014 Sierra 346RETS 5er BUB
Then-2002 Keystone Springdale 286RLDS TT
Nights camped in 2014-28, 2015-127, 2016-10