You need to remove the cog from the end of the cam shaft and that is the hardest job as it's done up tight.
I set the timing marks, remove the rocker cover and place a bit of wood along the head and I use my trolley jack bar and poke it through a hole in the cog and rest it on the wood to hold the cog stroll while you loosen the nut, you will need a long bar or torque wrench to undo the nut.
I just undo it a little and then set the timing to remove the cam belt from the cog. There is a white mark on the lower black plastic cover which you can line up and check the mark in the dissy with the rotor arm.
Picture of timing marks for a 1988 DX engine.
Be carful not to lose the woodruff key when removing the cog.
I smeared a little blue hylomar on the end cam cap as it's metal on metal.
Smear a little oil on the new seal and fit to cam shaft and fit cap.
Make sure you undo the cam caps nut in the right order as you can bend the cam shaft if not careful, order is in the hanynes manual.
Place the wood on the other side of the head and use the bar on the other side to torque up the cam shaft bolt.
Check timing marks again when putting cambelt back on.