Poorly silver birch

Good afternoon, we have moved to a property at a farm steading and we have few trees in the garden which are striving really well. However the silver birch looks rather poorly. It stands between a young oak and a leylandii tree and next to a small plum tree. we have looked at the leaves which are still sprouting, but just. Also, some of them sprouted and then died back. We have noticed some moss, fungi and bark discoloration on the tree as well. Could anyone please advise us on the next step what the options are? we would love to save the this beautiful tree. Thank you.