Slow Wan Link , what is the best way to prioritize traffic to certain app ?

Hi guys hope yall having good day Today

As the title say

we have ship in the open sea and the network inside connected to a VSAT through ISP , But it's very slow and very limited bandwidth ( 700 kbps ), I wanna prioritize the traffic to certain critical apps like email and voip phones .

What is the best way to achieve that ?

Thanks