Krishna does not dismiss the problem. He acknowledges that the mind is difficult to restrain, then gives a practical path based on returning, practice, and dedicated action.
Bring it back, every time
The practice is not having a still mind from the beginning. The act of noticing the wandering and returning is itself the training.
By whatever cause the wavering and unsteady mind wanders away, from that let him restrain it and bring it again under the control of the Self alone.
Build steadiness through repetition
A few sincere minutes each day are more useful than occasional force. Return to one support, such as the breath, a mantra, or remembrance of the Divine.
Meditating with the mind engaged in the Yoga of constant practice, not passing over to anything else, one goes to the Supreme Puruṣa.
Let action support the mind
When direct concentration feels difficult, the Gītā gives another entry: do useful work as an offering. Dedicated action gives restless energy a clean direction.
If you are unable to fix your mind steadily on Me, then endeavour by continuous meditation. If you are unequal even to that, let acts for propitiating Me be your highest aim.
The mind will wander. Each gentle return is part of the practice, not proof that the practice failed.