After tens of hours according to in-game statistics, I finally level up my engineer to level 25, therefore eligible for promotion. With this, I unlocked Deep Dive mode and The Forge terminal. Deep Dive mode will be the special kind of mission where instead of extracting after a mission in regular mode, I will be descending deeper into Hoxxes.

The Forge is the place in the lobby or the space rig, where we could build overclock for the weapon and craft accessories.

Got the notification

After this, I went to the Memorial Hall.

Choose the class to be promoted

Confirming promotion for engineer

Now, the first time I saw the confirmation message, I don't have enough credits, so I sell some mineral ores at the trading terminal

Congrats on the promotion, here are your rewards