One day you were not able to stand when the mother would make you stand and now you take part in race and can run.
This was not achieved in 1 day but practise over many years.
Even learning language English took you years from abcd to fluency.
If your mind is looking at form in world, tell mind that happiness is not in world ,but in Krishna .
Now make mind look at Krishna.
Nature of Mind is to flow continously.
Hence do not keep in pending once removed from world.
Immediately divert it to Krishna.
While you detach from world, do not focus on that there is no happiness in particular person/object but understand in general and immediately divert to Krishna.
You like say person A and mind goes to her. Do not think that there is no sukh in her but think that there is no sukh nor dukh in world and there is sukh in only Krishna. Hence attach in Krishna form. This detachment and attachment will happened in fraction of a second as mind runs faster then light.
Remember the example of girl who gets married. After marriage her attachment with maternal side asset goes away and attachment with husband side asset comes in as she now thinks that she will get happiness from husband side assets.
Similarly when we continously practise this art of detachment from world and attachment to Krishna, one day it will become firm.
Repeated thinking creates strong attachment.
Eyes see form, ears listen sound, noise smells.
In same way, divine soul desires divine happiness and material body needs material world.