If you’re asking now…it’s probably too late
If you’re getting a good price on rent, I would just let it go. The hassle you’ll have to go through getting the necessary paperwork probably isn’t worth the deductions you may get.
Try downloading the e-filing program and see if there’s a form in there you can fill out for this.
Honestly, if you have any tax related questions, head to your nearest tax bureau office like @Icon suggested. Firstly, make sure they can handle foreigner tax refunds, not all tax offices can. It’s not that they aren’t willing, it’s more they are not authorized to or do not have the staff that’s trained to do so.
The one just west of Taipei Main Station has awesome awesome service and all the people helping you speak very good English. Last year I went in to have them file my taxes because the e-filing software was giving me errors. I gave the guy all the necessary documents and IDs, he filled out EVERYTHING while I zombied on my phone.
If there’s no complications…you should be out of there in an hour. The level of service, courtesy and efficiency in there puts all and every government office in Taiwan to shame.