1. View porn whilst jelqing. Good short term solution to not losing erection.
2. Stop masturbating/ ejaculating as much. (If excessive, how to decide on what is excessive?)
3. masturbating yourself back to the correct erection level.
4. Jelqing at lower erection levels is alleged to be better for lengthening PE, so is it a worry. So if you lose your erection is it actually a problem?
5. Kegel, to push blood into the penis.
6. Split your jelqing from 1 session to 2 or more smaller sessions. And concentrate on their quality. Hopefully, you will see a healthier penis that can take a longer jelqing session.
How long is your jelqing session? Do you have an unrealistically high jelqing time length? If you lose your erection after an hour, then don’t worry so much. I can barely go past 15 minutes or so. I changed down to counting the number of jelqs to 100, 5 second jelqs and really concentrated on their quality.
Just a few answers off the top of my head. Hope they helped. :)