How do I fix this Trail Air suspension

I use 2 bottle jacks when I want to raise the trailer side for tire removal or other work like yours. I place 1 jack just ahead of the front wheel on the frame and the other just behind the rear wheel. I alternately pump one and then the other to raise side evenly without putting a twist to the trailer. Last 2 trailers I have owned weigh around 16,000# so just felt safer with 2 jacks. I also support with wood blocking or jack stands for additional safety. Randu

Jack and blocks or jackstands on the frame. I would replace all of the shackles unless there was a reason why those two failed.

I just replaced the springs and equalizers on my 5th wheel and 5 of the 16 shackles had elongated holes. The new ones that came with the replacement kit from Dexter are much thicker, more beefy...

I used a stack of 2X4s log cabin style to get my 4 ton jackstands high enough to reach the frame. Jacked up one side of the 5th wheel using a 6 ton bottle jack and my 3 1/2 ton floor jack. Got the tires off the ground and then placed the jackstands. Lowered the trailer down onto the jackstands after removing the tires. Then used the bottle jack and floor jack to control the axles (2 floor jacks would be better) to raise and lower as I removed and added springs and hardware.

Get some blocks and a hydraulic jack and raise it up jacking on the trailer frame.