My alcantara seats are the same - I did a temporary repair that has now lasted two years by :-
1) cutting the saggy bit in the centre of the “bubble”
2) then gently with fingers separated the alcantara from the backing material
3) use a felt material cut to the shape of the gap made with fingers between top layer and backing layer
4) cut strips of dressmaking “hem tape” - enough to cover the felt in 3) above - SWMBO uses this - it’s about a £1 for a large role of it - but it is only about an inch wide. Not found this stuff in large sheets.
5) glue the hem tape to the felt - I used a light spray of an aerosol impact adhesive - you don’t need much as it only to keep the hem tape in place on the felt piece whilst you insert it in the cut so it is on top of the old backing material and under the alcantara.
6) when this felt with hem tape “topping” is in place grab SWMBO’s Iron and a clean Tea Towel soaked in clean water.
7) make sure the alcantara top is nice and smooth and using the hot Iron on the wet tea towel on top of the alcantara gently work the iron from both sides of the cut into the centre. Don’t worry about overlap at the cut at this stage. The heat and the water/steam melts the hem tape and it then holds the material together and is flexible.
8) you should find the alcantara is firmly fixed to the new backing material - and I had an overlap of about a cm in the centre of the cut tapering out to the edges.
9) I then cut another strip of hem tape to match the overlap - recommend great care here as this will be visible when finished. Spend a bit of time making sure the hem tape is in place then gently place the wet tea towel on it and use the hot iron as before.
I was well pleased with the result!
You can only see the join if you really look.
I expected it to last a few months then new rips to appear - but to date it has proved to be a good long lasting repair that extends the life of an otherwise nice drivers seat that was really only fit to be scrapped.
If your seat looked as bad as mine did - give it a go - my thoughts were that I could hardly make it look any worse.
And the result is good!
