As has been suggested, either pull on the lanyards just inside the left front wheel well 'till the air is exhausted or, the more relaxing way is to just sit in the drivers seat and pump the brakes 'till the gauges read ZERO. Then your work is much easier. Again, while those push-to-connect fittings are "supposed" to be rather easy to service (disconnect & connect), sometimes they get a bit stubborn in the disconnect mode. When you push on the hose, you more than likely won't feel any movement, even though you're actually moving them a micro amount.
But, again, while holding pressure on the hose towards the valve, then push the small collar also towards the valve. You should feel it move very slightly towards the valve. If so, you can, at that point, while holding that collar with pressure towards the valve, simply pull out the hose. If there's any dirt/dust/oil etc. around the hose you're working on, simply wipe it off prior to servicing it. Good luck.
2004 ITASCA HORIZON 36GD, 2011 GMC Sierra 1500 4x4 Toad '18 Honda Africa Twin Adventure Sports DCT
Retired-29.5 yrs, SDFD, Ham - KI6OND
Me, Karla and the Sophie character, (mini Schnauzer)