Shimano fd-m510 front derailleur spring is stuck

Here is the link for front derail...
https://www.amazon.com/SHIMANO-XT-FD-M786-Down-Swing-Derailleur/dp/B007HDMY2U/ref=sr_1_1?dchild=1&keywords=shimano+xt+front+derailleur&qid=1591136571&sr=8-1

Can't tell what's wrong without knowing everything you've done. Try just going through the Park Tool procedure from start to finish, skipping no steps. http://www.parktool.com/blog/repair-help/front-derailleur-adjustment Front Derailleur Adjustment

I’m happy to help further over the phone at https://www.6ya.com/expert/donald_f2ed37026a3ac881

Derailleurs have a return spring in them that will always return them to the smaller cog (whether it is front or rear). The derailleur cable resists this spring tension. If your front der. is on the large ring and will not shift to a smaller ring then it could be a couple things. First, too much cable tension preventing the spring from returning the derailleur to a smaller cog. Second, you low limit screw is set too far in so the derailleur cannot travel back to a lower gear. This will be evident if you shift to a smaller cog, the derailleur does not move and the cable becomes slack. Third, something else is preventing the derailleur from moving, perhaps the derailleur was moved when installing the new crankset and it is getting hung up on a tooth of the large chainring, there could be some foreign matter lodged in the derailleur spring preventing it from operating, the spring could have broken so there is no longer enough tension to move the derailleur back to it's "home" position. Good luck.

http://www.parktool.com/blog/repair-help/front-derailleur-adjustments

We don't stock anything but advice.

Do they have Google where you live? Or a Local Bicycle Shop? Or online shopping which makes physical locations moot? "UK" doesn't narrow it down much.

When shopping for a front derailleur you need to know several things: braze-on or clamp mount; if clamp, seat tube diameter; top pull, bottom pull.

Don't fiddle.

http://www.parktool.com/blog/repair-help/front-derailleur-adjustments

Crank - No problem
Chain - No problem
Shifters - Compatible only with Shimano R440 or R443 front derailleurs

If you use the R443 front derailleur than it will work with the chain, crank and shifter.

http://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/FD/EV-FD-6600_6603-2349_v1_m56577569830608807.pdf

http://techdocs.shimano.com/media/techdocs/content/cycle/SI/SI_5JE0B_001/SI_5JE0B_001_En_v1_m56577569830616213.pdf

log onto Shimano.com, it is probably the limit screws (the two screws that limit travel) or you have a faulty ratchet in the lever, try the shimano website anyway they have great tutorial and manual support

Check Shift Lever for cable movement(Cable may be trapped) / Check cable lock nut on back of the derailluer(this may be loose)/ Check derailluer movement in/out with fingers(this checks the spring).