The first step when dealing with psoriasis
scar is to prevent further scars from forming. You can do this by making sure you are getting the best possible treatment for your psoriasis. The treatment for psoriasis these days is better than it has ever been, with numerous exciting and effective medications on the market that give excellent results even in severe cases. If you have active, severe psoriasis and have not talked to a dermatologist
recently about your treatment options, I suggest that you do so.
Regarding the scars that you already have on your skin, I think it is important to clarify if these are actual scarred areas or just areas of skin discoloration (for example, skin that is lighter or darker than the surrounding skin). If the latter, then this is not actually scarring but is an example of post inflammatory skin color changes. These post inflammatory changes, fortunately, do tend to get a lot better over time (weeks to months) and often to not require any treatment at all, although sometimes a dermatologist can give you a cream to help smooth out the color differences.
On the other hand, if you have true scarring, then you will need to talk to your dermatologist to see what options are available - these might include resurfacing techniques such as dermal micro abrasion or laser based treatments.