What can I do to remove the indentions on my left buttock and side of thighs? (Photos)

Most likely the cause of indentation is contractile scar tissue.
This means the contour will not be corrected by simply adding volume.
The contractile tissue needs to be removed in conjunction with volume augmentation.
This is fairly tricky and partial improvements are probably most realistic.
It’s done with the procedure called Subsicion which can be done with a device called Celfina though the device is not necessary.
Ideally at the same time the area is augmented either with grafted fat, fillers or both.
Avoid simplistic approaches like just injecting filler or fat grafting.
Without dealing with the contract dial forces the counter cannot be corrected.
There’s no one particular type of Doctor Who has any particular magic procedure for this. You simply need to find those who have done it before for other conditions like cellulite with good outcomes. Finding the right provider may take having a few consultations.
Both dermatologist and plastic surgeons are probably appropriate to ask about treatment options.
Best,
Mats Hagstrom MD