I am new to this forum and new to owning a hermit crab whom I have named Tiko.

A friend of mine was giving away their hermit crab and I offered to take it. My friend only had it for 3 weeks but kept it in a jar with sand & food.... I am learning how to properly care for it and provide a better environment. So far I have a tank, I am tracking temp and humidity, I have de-chlorinated water, sand, a sponge, a climbing apparatus, & food. I have to get salt water and some shells. I have had it for about 5 days now, I do not believe it has eaten anything and the last three days it has burrowed.
Although I have read burrowing is normal behaviour, I worry if those three weeks in poor conditions could have lead it to die?
Any advice or opinions are appreciated!
Thanks!