First, make sure no voidwyrms are nearby, as they will try to kill you. Next, pet the Astrodelphis. Finally, put element in the last slot of your hot bar and start feeding it to the Astrodelphis. Thanks for reading my tip!
U have to pet it and feed element. The amount of element goes up each time u have to feed, but the taming bar will fill up faster. Easy element u can gather by using an anky or pickaxe on the blue crystals in the space between the bridges. In the center of the map
If you need to keep it in one place you can use dinos to trap it. Dinoes swim in space like they do in water so create cage of dinosaurs ( make sure they are big, heavy and have a lot of health because the astrodelphis
will attack your dinos ) then leave a gap for the astrodelphis to get in. Make sure all of your dinos are on passive and lead an astrodelphis in the cage by getting it's aggro. Once you have trapped it the astrodelphis will not be able to escape unless it kills or moves your dinos out of the way.
BEWARE OF FOOD DROPPING. Not sure if it is a glitch but within a minute or so of taming it was starving. Filled with with a few stacks of meat and it ate them all and starving within another few minutes. Bring extra meat.
(I’m writing this off my own experiences from taming it, hopefully it’ll be helpful to you, the reader!) For taming you need to trap it (most preferably 5 gates in length) it can be very difficult to trap but as long as you get a straight angle you should be fine. They can attack and their attacks have massive knock back (making trapping more difficult). For taming you need to pet it (sometimes more than once) and then feed it element which increases each time you feed it (1, 3, 5 and 10 then it resets back to 1) Make sure you keep petting and feeding since it can loose like 30% if you stop for a short time. Element can be found during purple drops in the blue-ish area. Hope this helps.
What I do... I use Helena to scan it to see its lvl bc I have trouble with the spyglass on space biome..I will aggro it and lure it into the bridge and take it up a bit so it stays out of the space biome and not have to worry about voidwyrms... once it is where I feel is far enough I will tek speed run away and leave render...I will then pet and feed it