All I can say besides the standard formula of grinding Argunite for 910 pieces with craftables to hit LFR requirement for Antorus to get the ring, is good luck.
Only completed Sigryn with my Enhancement Shaman while having Prydaz and Roots of Shaladrassil at 925. Had attempted it before at 870 without any legendaries which was basically torment and it took me 3 attempts to down it with the higher ilvl. At average skill-level, the key is patience and sinking in enough time to get the gear (Obviously, it would be good for you to watch the videos as well)
In my case; per the dps I can pull with them, I basically suck at playing dps casters compared to melee and, I am basically aiming to get 930 (With 915+ relics and NLC being 3-2-2) on all the specs before setting foot back into the challenges for my other chars and specs.