Dose is 57 mg per pound of body weight, twice a day for 5-7 days.
It won't mix well with water. I empty the capsules (figure out how many doses for the treatment period, and do the math for the birds weight to see what the mg per dose will be, then empty enough capsules into a small bowl to make up the amount. If your bird was 6 lbs then each dose would be 57 mg x 6 = 342 (round up to 350 for simplification). So 7 capsules of the 500 mg would give you 3500 mg, divide by 350 for each dose, and that would give you 10 doses, which will give you 5 days of treatment. Then mix with a small amount of softened (not melted) coconut oil, enough to make the number of doses you need, in a size you can give. If you make each dose 1/4 tsp you would need 2.5 tsp of coconut oil. Or you could go as big as 1/2 tsp per dose, whatever you are comfortable with and can divide evenly. Mix it all up really well, make sure the medication is well and evenly distributed/mixed. Then divide up into the amount of doses you figured for and freeze them on parchment paper. You will have custom 'pills' that go down easy. Hope that all makes sense (check my math!) Put in the beak and push back a little, she'll swallow. Break into half, or smaller if needed, just make sure to give the whole dose at one time.
Having said all that, salpingitis often does not respond to treatment, and amoxicillin isn't often effective. Might buy some time, hard to say. Usually for salpingitis something stronger is recommended, like Baytril (enrofloxacin), but that may not provide a cure either. If you want to get enrofoxacin, the oral is available from pigeon suppliers without prescription, the injectable has to be gotten from a vet.
One source for the oral:
https://jedds.com/products/enrofloxacin-10
