If you are unable to pull off the seam tape by hand, you can use an old toothbrush to brush off the flakes off. For stubborn areas you can use a solution of rubbing alcohol, dish soap, and water in a small basin or bucket. Wear gloves and soak a rag or washcloth in this solution and use it to wipe away the degraded seam tape. If a few flakes remain here and there, that's OK. You can apply the sealant over these areas. The idea is to remove as much of the flakes as possible, but it's not absolutely necessary to remove 100% of it.
How can I remove old damaged seam tape?
If you are unable to pull off the seam tape by hand, you can use an old toothbrush to brush off the flakes off. For stubborn areas you can use a solution of rubbing alcohol, dish soap, and water in a small basin or bucket. Wear gloves and soak a rag or washcloth in this solution and use it to wipe away the degraded seam tape. If a few flakes remain here and there, that's OK. You can apply the sealant over these areas. The idea is to remove as much of the flakes as possible, but it's not absolutely necessary to remove 100% of it.