Used to do this for a living. Waterwell Service.
Blow the well, we'd rent big compressors out that you see running around fall blowing out irrigation lines, drag it out with one truck and use the well service trucks to go down on 1" steel pipe to the bottom and hit it with the air, the whole column of water will shoot out of there, stand back and cover up things you don't want covered in red/black and more. It will go 60-80' in the air sometimes, it's spectacular. You can go down on 1" carlon pipe too but use a 10' length of steel on the bottom so it stays in the hole when you let the air at it.
New water rushes into the well, let it fill up and you do it again and again, you may notice your pipe now going further down the well each time as your lowering the level of solids at the bottom. Blowing it for an hour or three will get all the solids out, mark the intital start point of where you hit bottom with wrap of electrical tape on the pipe. This alone will likely increase production and open some things up, especially if you removed 10' of muck from the bottom but the air is violent and will dislodge lots of stuff down there.
Then you can do an acid job....pellet form acid in the 9 lb tubs i believe, go with 27-36 lbs of acid, it's lighter than water so it's in pellet form to get to the bottom of the well and start working it's way up. Let it do it's job for a few days. Then blow it again, or pump it out but easy to plug pumps...the acid will help open up those perfs to improve the inflow again.
When all said and done you can do a shock chlorination. 5 gal of the industrial sodium hypo (much stronger than javex) and it's heavier than water. We would premix in a tank of 300 gallons of water and dump the whole works down, false head forcing chlorinated water back out into the aquifer. Let sit for 24 hours and then pump out.....hours of pumping out, throttling pumps to match if you get to suction etc.
All of it is messy and will be removing a lot of
Drill a new well nearby and you'll tap into the same aquifer anyway, if it was a proven 50 gpm well at one point and just been left neglected for a long time it may be worth starting there, even if you end up having a driller pull the liner for new or rework the hole how they see fit?
And if you take it that far, make sure it's protected after so no more contaminants can get in from surface.
Hope that helps.
Note: 1 gpm is 1440 gallons a day. You can live on that with a reservoir, even a 300 gallon bolt together fiberglass in the basement. Installed plenty of those type up to 750 gallon when drought of 2000-03 was happening. Lots of wells dropped to below half normal production in that time. We also burried lots of 3500-5000 gallon fiberglass cisterns for bigger operations/ranches also. But a typical house can easily live off a 1 gpm well if you store it. No appliance works off 1 gpm so you have to store it.