Not much you can repair except "bad caps". If your board is damaged with a deep nick over the circuitry, then you may not be able to repair more than one layer of damage.
o1die speaks truth cause these days motherboards comprise of up to at least 4 layers with circuitry between each layer. By trying to fix a damaged motherboard, the circuitry between layers can easily be damaged.
o1die just told you. Apart from damaged capacitors (assuming you visually detect them) and other visual signs of damage, there is no general knowledge about how to repair modern, multilayer motherboards.
As Makers of these products upgrade them they tend to makes it much difficult for anyone to fix them when a certain degree of damage is done to them leaving the complainant with no other option than to buy a new one