Replacing a crankset after 1 hour!

I know this is late and you’ve sorted this now, but the easiest thing to do is replace the arm and ditch the pedals. New arm would cost around £10 and get some half decent pedals. Can get Burtecs for around £40 half price from £80 from most places. This may help someone??

You could replace the crank with any Shimano 2x9 crank for a square taper cartridge bottom bracket (with the same chainring sizes are crank arm length or course). If the bike is equipped with an Altus groupset then an Altus 2x9 crank would be a reasonable choice.

There is a bit of an annoying wrinkle to this, different square taper crank models require different specific axle lengths to achieve the correct chainline. The existing bottom bracket axle might not be the correct length for the crank you choose.

As an example The Vitus Nucleus 27 VR page helpfully tells us the the BB axle length is 113.5mm. The Altus FC-MT101-2 crank needs a 'LL123' code bottom bracket axle which I think is actually 122.5mm.

Often it's easier to buy and install a crank and the correct bottom bracket at the same time. This also opens up the possibility of a 2x9 crank with a Hollowtech II external cup bottom bracket, which I think are in the Acera line and would be an upgrade.

Special tools are required to remove and install bottom brackets, and a crank puller is needed to get crank arms off square taper axles. Bottom brackets and crank arms should also be installed with a torque wrench. It's especially critical to get square taper crank arms tightened properly.

If you had a an issue with pedal installation you'd probably want a bike repair shop to do the installation for you, and they will of course have the tools.

It might be possible to make a new thread using helicoil. It is a job for a good bike-shop but should be cheaper than a good pair of cranks.