Silent Field - Annihilation

First tell us these things:
CEs you have.
Servants, levels and skills

Or else I'm wont know what to say

As stated its hard to give a specific answer not knowing what options you have my own strategy for doing it with all event CEs being Salter, berserker Sakata(Lu bu works just the same as a low rarity option) and support waver clear the first 2 waves with normals should take about 6 turns meaning you now have wavers abilities off cooldown for 100% charge on one 40 on the other or 70% each in total essentially guaranteeing that you'll have both NPs up to nuke Jalter and Karna at the end.

It is a high level mission though so if you're lacking in high level servants it may difficult to impossible.

Disclaimer - This is just theory and I haven't tested it.

Now if you just want to clear it, it should be possible if you can borrow a friend's Cu Alter and fill the other slots with servants having Target Focus skill. You could give them Lifesavers CE for more survivability.

Start by clearing the first two waves and building up Cu's Np gauge and let the other servants soak up the damage. Before you enter the last battle make sure Cu's at 100% Np and all your other servants are dead. This is important. At the start of third battle, use Chaldea Mystic Code's Atk Up and Evasion and do a NPBB chain on JAlter which should kill her. Do a BBB chain next to kill Karna. Just in case, use Cu's 2nd and 3rd skill before this and it'll give you an extra turn.