How can I void my old visa while in Ho Chi Minh without going back to Tokyo?

Pretty sure a visa can't be voided. Either wait for it to expire or use it

It is simple. You come to Thailand with this TR visa and departure again. It will be automatically used this Visa.

You either need to get the embassy in Tokyo to void your current/valid visa (which may be difficult to do) or wait for it to expire then apply then.

It looks like it

Japanese embassys have been giving out Education visas to DTV applicants for some time now. It makes things really hard as the applicant then has a visa which is kind of not valid as its attached to a DTV gym that mostly are not licensed Education visa schools. So impossible to extend beyond the 3 months. Its really strange that they do this.

However the Japanese embassy in Tokyo contacted us today about 2 applicants and we were able to explain to them what's been going on. I think they might start actually issuing DTV now.

You have been granted a Tourist Visa. It looks like they will not process your DTV until it's canceled (or expired). If you do not want to wait till expired contact the Embassy in Japan and ask them to cancel the visa.

Yes