To revive an overwatered tree, allow the soil to dry out and improve drainage and aerate the tree roots if possible.
And stop watering of the tree for awhile until it starts to revive.
Most trees can recover from overwatering if the overwatering is noticed soon enough and in most cases the tree will begin to recover from the overwatering within a week or two.
Aerating the soil around the tree roots, helps to improve the drainage of the soil and create more air space for oxygen to reach the tree roots.
You can use a garden fork or a special soil aeration spike to create air pockets and if the soil is compacted, you can amend the soil with organic matter like compost or well rotted mulch to improve drainage and air circulation.
If you have some mulch around the tree's base you can remove the mulch temporarily to allow the soil to dry out and prevent further moisture retention.
An over watered tree will look like yellowing or wilting of the leaves and the over watered tree may also have fungal growth around the base or algae or moss around the base of the tree.
The soil around the base of the over watered tree will also be consistently wet and even possibly be soggy.
And with an over watered tree, new growth may wither prematurely or even turn light green or yellow and the leaves of the over watered tree may even appear green but be brittle.
The most common signs of an overwatered tree are leaves turning yellow, which can also be accompanied by drooping or wilting of the leaves.
The soil around the base of a tree should be moist but not overly saturated or soggy and if the soil around the base of the tree is overly saturated or soggy then the tree is being overwatered.
Any excessive moisture can also encourage the growth of fungi such as algae, moss or mushrooms around the base and the trunk of the tree.
And even if the leaves of the overwatered tree are green they may be brittle or even break easily which indicates that the tree is overwatered.
And if the tree appears to be wilted even though the soil around the base of the tree is wet, it's a very strong indication of the tree being over watered.
In some cases a tree will naturally recover from being over watered as long as you stop watering the tree and allow the tree to use up the water and recover.
If your tree is over watered you should scale back on the watering frequency immediately and allow the soil at the base of the tree to dry out between watering's.
On average it takes an overwatered tree 7 days to 14 days to recover from over watering.