Your specific gravity is FATALLY low for this star. This is a characteristic death from acclimation shock which occurs within a month of introduction to a tank.
Most Linckia species stars DO NOT take to spot feeding. This should not be counted on. If you are lucky, you're VERY lucky...I would try to spot feed, but the overwhelming majority show no interest at all.
A blue Linckia requires the following, IMO, to have a chance of survival. Most do not survive more than a year, and success for less than a year should be taken with this in mind: it takes a healthy wild caught star around 8-12 months to STARVE TO DEATH. With no obvious signs of problems.
Necessary:
- Minimum 6 month old tank with PRISTINE water parameters (esp low nitrates, specific gravity 1.025-1.026, stable pH around 8.3, proper alk and calcium.
- Minimum 100g, but more importantly 150+ lbs of LR. Again, MOST CAN NOT BE SPOT FED and need LR to feed on.
- LONG slow acclimation, via a drip method...but if the specific gravity is too low it won't matter too much, IMO.
I am afraid there is little that can be done for this star, other than to hope it last long enough for you to try and get specific gravity into a suitable range (which should take several days at least). Even then, most of the damage has already been done, and it is unlikely, IMO, to recover from this.
Linckia and Fromia stars have very specific needs. Most are not suitable for this tank size range, IMO, and will not last for more than a year to 18 months.