How to max out Tsumitate NISA in December?

I have most of my NISA quota left unused and want to use it before the year ends. I'd like to add to the same funds I've already invested in, but I can't figure out how to make a lump sum contribution for the remaining balance. Can someone please help? I'm using Rakuten Securities.

I have shared screenshots for reference:

https://preview.redd.it/130thtq70o8g1.png?width=750&format=png&auto=webp&s=7ee5d80e2e874f9e5db1f39730889d958505edc1

https://preview.redd.it/5a9wr6ta0o8g1.png?width=1074&format=png&auto=webp&s=1aaa98bc1188b71255be423afe1f61c8c92e8d4a

by Maximum_Intern9873