What is the ruling on performing ghusl for janabah while having a wound on the right leg that has been covered with a bag, and must the prayers be repeated?

It is obligatory to wash the entire body during the ritual bath (ghusl). If there is an exposed wound, it must be washed with water. If washing is not possible, then wiping (masḥ) should be done. If wiping is not possible, then tayammum (dry ablution) should be performed. However, if the wound is covered, only wiping is required. If wiping harms it, then tayammum should be performed.

Based on this, your previous ghusl was invalid and did not remove the state of impurity. However, you are not required to repeat past prayers due to your ignorance of the ruling. You are now only required to repeat the ghusl and perform the current prayer.