Self-employment and employment in same tax year

I was self-employed throughout 2016, and up until 1st October 2017. I have paid self-assessment tax on my 2016 income and preliminary tax for the 2017 income.

I became employed on 1st October 2017 and from there on was taxed via PAYE.

From October - December 2017 I was paid by my new employer and was on an emergency tax rate for these 3 months so I need to reclaim this but I can't work out how to request this via Revenue online, has anyone been in a similar situation and can advise please?

I would think that you should submit a Form 12.