This is the encoder strip. it is printed with dots that tell the print head where it is. You need to reattach the left hand side. You need to find the hole in the metal framework at the same level as the strip. The end goes through the hole and attaches to a metal tab. The metal tab is J shaped so that it holds the tape in place. I found that the best way of doing this was to put the tape horizontal through the hole and then rotate it back to vertical. There is one end which is spring loaded to maintain tension. On my printer this was the right side. I found it was best to get the spring loaded end fixed first and then attach the non spring loaded end. There are some descriptive guides if you google encoder strip.