Hello,
What do I understand, the board's VGA connecter is just a simple connector which attached to the I/O pins of the FPGA which you need to apply a VGA video generator function in your logic design.
I found a reference for the board which has a VGA demo under the Demonstrations/VGA Pattern folder. You can refer to the TerASIC system CD "DE10-Lite_v.2.1.0_SystemCD". In case you do not have it, the TeraASIC support CD ISO image available from below link:
https://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&CategoryNo=234&No=1021&PartNo=4#contents
I also found several website links available that you might want to check out for the tutorial that might help you:
https://habr.com/en/articles/707224/
https://www.ece.ucdavis.edu/~bbaas/180/tutorials/vga/
https://www.youtube.com/watch?v=mR-eo7a4n5Q&ab_channel=Dom
https://www.youtube.com/watch?v=WK5FT5RD1sU&ab_channel=Toni