The advice I would give someone looking to become a soulbonder is this:
pick one character, a character who resonates with you, and you have a lot of feelings for. Not a character necessarily that you think is a lot like yourself, but a character you admire for their strength, or sympathize with for their problems. Essentially a character that you have strong “feels” for.
Ruminate on that character. Try to ‘get to know’ them as deeply as possible. View/read/listen to all their source material, and any fanfiction that speaks to you as 'true to character’. Collect pictures of them. Do anything that keeps your mind focused on them, as if calling out to them. Keep the character in your mind during the day, maintain your feelings for them.
Ask during the day (in your mind) what would X do? What would X want? (Getting ice cream? ask them what flavor they want. Having difficulty with something? ask what they would do)
Eventually if you’ve established a bond, they will answer back from the back of your mind. It may be faint at first, and you may be inclined to dismiss it as you pretending, but don’t do that. Keep asking questions and talking back when you receive an answer. This will strengthen the bond.
Another way to do this would be to do it on paper instead of your mind. Write a scene with you and the character, as descriptive and detailed as you can make it, and write a conversation back and forth between you. Eventually, if you’ve established a bond, you’ll start to 'hear’ their answers before you write them.
If none of this works after a while, pick a different character. It may be that the character you’ve been focused on just isn’t receptive/isn’t the right bond for you right now.