Generally, it's very unlikely that speaker from a laptop (little thin strip) will be interchangeable to replace monitor speaker (larger mounting and power).

Specifically, any type of hack or modification may render your working device to become unusable.

Your post is vague.

Are you asking how to physically change speakers from Laptop to a Monitor?

Or are you asking how to tell the operating system which speakers to transmit audio through?

We also need to know what specific Laptop model, operating system, and what specific monitor model.

If the monitor has built in speakers, then you can go to the Windows sound settings and set the monitor as the default playback device. However, many monitors do not have speakers, so installing separate speakers is a better option.