You are helping - they clearly need the additional training, and you’re doing everything you can to supply that. Their job can’t be relying on you.
They shouldn’t (and almost certainly don’t) have delegation authority.
For corporate bingo, the keywords are upskill, cross-training, and bus factor.
Don’t show. Guide them to do it themselves. Never be the one to actually do it beyond the first time.
If they still refuse to learn, make them take notes. Make them read to you their notes from last time. Make them tell you what each step is and means.
Make asking you the hardest option for them to get what they want.
Thinkpads are extremely well documented. For how to repair/replace parts, you need the HMM. Just Google for “Thinkpad t14 Gen 1 HMM” and you should find the official PDF on their site. That will tell you, step by step, how to replace the keyboard.
As for the part itself, you can again check Lenovo’s site for all compatible parts (FRUs) and find the item number and details. While I wouldn’t recommend buying directly from them due to cost, this should give you the information needed to find it elsewhere. eBay has tons of Thinkpads being sold for parts, and many of these will be parted out. You should have no issues finding what you’re looking for.