My patio cover is leaking where it is attached to the house, how do you fix it.

The cover is aluminum with all aluminum edging?

The house fascia SHOULD be higher than the edging if it was installed correctly(to allow the water to pass over the drip edge and on to the top.)

If it was not installed this way,(or even to the roofline) a flashing will need to be installed,one which transitions the house roof to the patio cover.

The new flashing should only be hard nailed to one surface,either the house(which is the normal way) or to the cover,but never both.The 2 rooflines move differently(horizontally) with heat and cold,that causes ripples in the flashing if both are hard nailed(eventually causing it to fail)

Use high strength silicone caulk on the base of the flashing after the upper part is hard nailed UNDER the shingles(or whatever the roof consists of)