In Hanoi rental agreements many odd jobs are a landlord’s responsibility. For gardening, painting, plumbing or electrical work not covered by your lease, your landlord shoud be able to recommend help.
Most laborers do not speak English, so it is useful to have your landlord or a local friend help in the process of hiring a handyman or gardener, and in giving instructions.
Word of mouth is the best, and often only, way to find help, as well as bulletin boards at grocery stores, cafes and schools. You can try the classified page of the New Hanoian website, though listings offering help for odd jobs are not common: