The homework solutions are submitted to a platform called "Gradescope", see this tweet and the tweets above it in the thread for more details:
https://twitter.com/andy_pavlo/status/1564305764730167303
Also, I should mention there is a very large (unofficial) Discord server (+1,000 people) where some of the TA's from this DB course and myself hang out if anyone is interested:
And if you find database engineering interesting in general, I might also invite you to come hang out in Phil Eaton's hacker-space Discord, which is quite good: