Hi,

First of all find and get which field links both these model, probably there will be a Many2one relation between these two models.

Using this related field either you can use compute or related fields.

Suppose if you take the example of sale order and sale order line, there is a many2one field named order_id which connects order line with sale order.

So if you need to get the customer in the sale order in order line, you can define a related field in order line like below,

partner_id = fields.Many2one('res.partner, string='Partner', related='order_id.partner_id')

Watch:  https://www.youtube.com/watch?v=poDGUKM-K7Q

Thanks