You could just try to reseat the Trackpad cable, but you likely need to replace it. It's not that hard to do! Here's the needed cable [https://beetstech.com/product/ipd-trackpad-flex-cable-923-00518|Trackpad Flex Cable Apple P/N 923-00518] and here's the guide to put it in [guide|45138]
Often this is the root issue. Make sure to clean the surfaces fully as any grit will over time damage the cable. You also want to use an OLD BIC pen ink straw to help in forming the folds as you don't want a hard crease as that weakens the thin foil wires. Leave the adhesive protection on so you can place an index mark using some masking tape across between the battery and the cable so you have the same amount of slack on each side of the battery. Each time you discharge or charge your battery it will swell! So its important to have enough play of each side of the cable. Once you've got the index mark carefully peel the cover an press from the center outward in the cables direction.