If you lowered your PeD to catch the ISS orbit, then, you'll have this common point, right? You will reach the ISS in that point, so, wait untill you are there, then when you are on that point look at the "DTmin" row in your Sync MFD: there is a number that you have to decrease to zero. Try to burn prograde: if the number decrease, you can continue, it the number increase you have to burn retrograde taking care to don't lowere your apoapsis below the upper limit of the atmosphere or you WILL BURN! Eventually, when you reach the zero value, cut off the engine, look at the numbers rows in the right of the MFD, there is a yellow row of numbers. These are the times relatives to you and the ISS for when you will rendezvous. If the "0" row is highlighted you will catch the station in the orbit you are in, if the second row is highlighted you will catch it in the next orbit, third row two orbits etc. etc. At the end, if you do all perfect, you will see the ISS in front of you! Good luck!