Start by finding the "extra" rope on the drum. There should always be a length of extra tension rope of about 2 meters or more that remains after the tension rope is tied together. If your drum has no horizontal weave at all (horizontal weave is what tightens the drum) the extra length will be close to the connection point of the tension rope. If you have horizontal weave already, it will be at the end of the weave. Sometimes it will be tied off in a kind of handle for the drum, sometimes it is just wrapped around the collar of the drum, sometimes it is tucked under the tension rope. Whatever the case might be, find it and untie any knots until you have a nice straight piece of rope at the end of your horizontal weave (or at the "beginning" of the drum if you have no weave yet).
Once you have this rope free it will be your "Tightening Rope". I also refer to it as your horizontal weave rope. It's the white rope in the photos. Just to reiterate, I simply tied a piece of white rope on a black rope drum so you can follow the white rope easier.