How can one perform ablution for prayer when there is severe pain in the left hand following a lumpectomy for a benign fibroid in the left breast, without affecting the wound site?

If you are able to perform ablution (wudu'), it is obligatory for you, even with the help of another person, as long as it does not affect your wound. If you are unable to perform ablution due to the wound and cannot find assistance, even for a fee, then perform tayammum (definition) (dry ablution). If the problem is only with the left hand, you can perform ablution using your right hand to wash your face and hands, wipe over your head, and wash your feet.