A dog of this age will be well set in its ways and after all that’s happened recently the last thing the dog needs is for you – a stranger to now start putting it through a schooling.
Depending on the dog, I would give it a six week get-to-know-you period where all you do is take it for good long walks on the lead.
This is usually sufficient to establish a bond, but dont be surprised if it takes longer. Be patient.
Theres no earthly point rushing matters because you wont get a dog to respond to your training if the bond isnt yet there.
It needs to get to know and trust you. Its not always important to have the same whistle used previously because we all have our own way of blowing a whistle and its this that you will have to experiment with.
Most gundogs are trained to a fairly standard format i.e. one blast to stop, two peeps to turn and a series of peeps to come back.
The commonest whistle out there is the good old 211 which is stocked by most gunshops.
Its not expensive either, so buy two or three to ensure ones always at hand.