Random(number) takes one number. It generates a number between 0 and a number.
RandomInRange(number, number) takes 2 numbers, a lower and an upper. It generates a number from the one number to the other.
You can create an object using a random number to choose from an array with the list of object names.
Another option is to name your objects with the same name plus a sequential number like turtle1, turtle2, turtle3 and put them into a group. You could then use:
Create an object by name “Turtle” + ToString(RandomInRange(1, 3)) from the group
https://wiki.gdevelop.io/gdevelop5/all-features/expressions-reference/#mathematical-tools