I had carpet laid about 9 months ago. There is a seam showing. I thought the guy would come back are fix it but he never did.

I believe it will be hard to get anyone to come for that.

Is there anything I can do myself.

I believe the reason why the seam is showing is because he didn't heat the seam long enough because he blew a fuse when using his tool for heating the seam.

Any tips will be appreciated.

You can try heating this area with your household iron, but it would have to be done from the wrong side of the carpeting to be effective. You could try it from the front or right side of the carpet but you'll have to put something between the iron and the carpet - like a heavy piece of paper like a brown shopping bag. Hold the iron down as hard as you can on the surface and then slowly move the iron around for about 2-3 minutes. That just may solve your problem. If it doesn't solve it - keep calling the company who originally put the carpet down for you and insist they come back and finish the job.

What type of carpet is it (plush, shag,berber etc). Where is the seam in door way or is it joining to pieces of a room together. AlsoI would be able to advise you better if you could post a couple of pics. It could be an installation problem as you stated or it could be a carpet that's just difficult to hide seams in. The shorter the nap and tighter the weave the more readily seams show. Cross cuts on berbers can be difficult as well. Post some pics if you can and Ill try to help. If you can't post pics then tell me as best you can what causes the seam to show( separating, strings sticking up, etc)

I'd be real hesitant to try using a household iron for this... by the time the iron's hot enough to melt the glue you may have already melted the face pile. In general, installers will warrant the seams to hold, they will NOT assure complete invisibility.