The OnRoute route optimization API offers two different solutions for that:
1. Focus on a type of resource: If you are looking to assign a specific type of resource to an order, e.g. a cooled truck to deliver frozen goods or a field engineer with specific skills for a specific problem, you can use tags. Put the same tag in both the order and the resource profile and the solver will match these automatically. You can make these tags 'hard' or 'soft', and assign a weigh to them to further finetune your solution.
2. Focus on an individual resource: If your are looking to have a specific order (e.g. for a specific customer) executed by a specific resource (e.g. always the same nurse) you can use job relations, more specifically the same_resource relation.