Hi and welcome to the forum.
The standard advice regarding HiLos and towing, is,"NEVER tow a HiLo with the top up. You will damage it".
So, you've experienced the "damage" part, and the first problem will be to get the top back up. A common way to raise the top when the lift system is not working, is to use farm jacks. You would need two of these, to raise the side that has dropped. An alternate way is to get help from several strong neighbors. With enough muscle, they could probably lift the side that has dropped.
Then, you'd need to keep it there. A temporary way is to use two 2x4s, cut to the proper length to go between the top and some part of the lower half that would support it. Later model trailers have what we call "outriggers" - metal beams, about 2" on a side that extend at four points from the bottom half. The top rests on these when it's down for towing. You could place the 2x4s between the outriggers and the top to hold it up. If you don't have outriggers, put the 2x4s on whatever you can find, even the ground if necessary.
You will have to cut the 2x4s to the proper length BEFORE you get the low side raised. Use the side that did not collapse to determine the length to make them.
Now the final part. If you plan to leave the top up, you will need to find out how the previous owners modified it. You may be able to tell by looking, but you may have to contact them to learn how they did it. Whatever way they used, it does not seem to have been particularly sound.
Of course, the real advantage of HiLos is that they tow low for reduced wind resistance, better stability and so on. SO, you would really be better off repairing the lift system so that it worked and remove whatever was installed to hold the top up. That would be a serious undertaking.
Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH, Progressive Dynamics Converter, Fan-Tastic Fan
2014 F150 Platinum 4x4 3.5L EcoBoost SCrew