You probably cannot repair the seam at all due to the fact that it is more than likely due to a process called delamition. That is when the primary and secondary backing on the carpet part due to excessive moisture, a manufacturing defect, or some other problem. If it can be repaired at all a short term fix is the best that can be expected and its best to leave it to a proffessional carpet installer so as not to further damage your carpet! I know what i'm talking about as my hubby is an installer & i have damaged carpet by thinking that i could absorb his skills by osmosis:) Hope i could help!