I really screwed up my template - HOW do it get the old one back

i had a template from which i do all my invoicing. i was trying to change the default font from times new roman (never figured out how to do that!) and picked some kind of custom formatting. suddenly, all my libre office writer documents turned into some kind of "paint document! i tried “edit file” and it asked me to save changes, which i idiotically did. now i can’t undo and ALL my office libre documents with the template i have slaved over for countless hours open in this ridiculous, unusable format. Please, can you help me get my old template back and have my documents open up the way i want them to again? (and can you help me lose the hated Times New Roman font as default?) thank you so much. my business depends on it.

MORE INFO on my problem: oh yeah. it also turned that template into a “read only” document and now i can’t open any of my other past invoices. they won’t open at ALL. i have gone onto “help” which just isn’t that helpful for the novice in answering complex questions. thank you.

You invoke your backup software and select the broken files to restore. You hopefully do backups at least every other day, don’t you?

i don’t do backup because i don’t know how on a Mac. that’s a whole 'nother question…
thanks for answering. and i have no idea what it means to select the broken files to restore… sorry. as i said, brand new on Mac.

I’m sorry. i am a pc gal who was given an old hand me down imac, with little time to reinvent the wheel or learn a new office program. i am not used to mac or libre office. i’ll probably love libre office once i understand it better.

i simply closed down libre office in the finder and reopened it. everything appears fine and working, for now. but i still would love help changing the default font. thank you and sorry for the false alarm.