1. Which one is correct? The meal was (salty / over-seasoned) last night.
It really depends on the meal itself. Salt is a form of seasoning just like pepper, garlic, cumin powder, coriander, and so on. If the person who cooked the meal put too much salt then one would say the meal was salty. If the meal has a very strong flavor and one doesn't know what it is then one can say the meal was over-seasoned. Either way, both can be used and essentially be correct. A salty meal is an over-seasoned meal; however a meal with too much pepper or too much garlic can also be an over-seasoned mean but not a salty meal.
2. Which one is correct? We need to (push back / put off) the meeting.
Pushing back a meeting is the same as rescheduling it for a later time or date. Put off can also be used in the same context. It basically means to delay or postpone but when it comes to meetings people usually say push back vs put off.
3. Meaning and usage of "make it into work"
This basically refers to the action of going to work. Example: "I hope I make it into work on time" is the same as saying "I hope get to work on time"
I'm not a professional teacher or tutor but this is a basic explanation.