1) Allow people to opt out. If you're still working you can opt out of paying into it from now on, knowing you'd have less SS benefits in the future.
2) Allow people who've already paid into it get their funds out, perhaps with some interest. Again, no future benefits.
Few people will stay into it, so nothing is "taken" from them. Most people will opt out/cash in. This will be a huuuuge cost up front, but it's do-able and IMHO a much more bearable pain than letting it get bigger & bigger forever and ever. The SS trust fund now has $2.9 trillion (as of end of 2018). How much is needed to payback to everybody who already put in?
If you allow people to opt out whos going pay for next months Social Security checks?
They can’t let people opt out because it’s a ponzi scheme. That would just hasten the collapse.