New Gear changer, cant find 1st

I have replaced my snapped gear changer thanks to the purchase of some circlip pliers. I marked the position of the connection rod thingy with tape so i could see where the nuts and position of the rod were. I can now not put the bike in first, 5th or 6th. Is it now just a matter of trial and error or is there something else i need to consider?

Sorry for posting two questions - the bike has been in a garage for 2 months while insrunace wrangles continue. I now have the bike back and started it today but it spluttered out after a couple of minutes. Is there a fuel line tap possibly engaged in the garage?

Merci.

Are you rotating the rear wheel while trying to engage the gears?
(I'm assuming you're doing this with the engine off.)