Just thought I would add to what Duc said, by telling you a bit about the grammar involved here. 지다 - is a auxiliary verb, that gives the meaning of "to become". Like, "It got cold." would be, 추워 졌어요. The grammar pattern -ㄹ거다 is the future tense, meaning something will be. 고 is the quotation particle. In this case the 다 in -ㄹ거다 is from the copula (이)다. And when the copula comes before the quotation particle it changes to (이)라. 알리다 is the verb to tell/ let know/ inform (literally the causative form of "알다" - to know). 주다 is an auxiliary verb that means to give/ or do for. So 알려주세요 is politely asking someone to let you know something. So, "Please let us know everything will be fine." is what it means, like Duc said.

모든 것이 괜찮아 잘 거라고 알려 주세요 let's me know you are all right هل انت بخير 모든 것이 everything괜찮아 질 be fine거라고would 알려주세요please let us know

tell (알려주세요.) that (거라고) everything (모든것이) is gonna be (질) fine(괜챦아). 거라고 -> that is going to be -> 질