First time doing income tax for extra income source

I'm a bit overwhelmed trying to figure out how to file taxes.

– I work full time and the company manages taxes on that side

– I made additional income from overseas which was paid through Stripe and then transferred into my Japanese bank account

– The total amount of money I made is less than 500,000 yen

– I do not have my own company. I billed them as an individual

– I have been in Japan for 8 years

– I am on a 5 year working Visa. Engineer/Specialist in Humanities/International Services

From what I understand, I have to file that extra money somewhere, and then fill out a year end tax adjustment form that my main company provides