So, you overexposed your film by 1 1/3 stops (if you're actually exposing for ASA 160, you hint at actually exposing for a slower speed). As this isn't a whole lot, there are two things you can do:

1. Process the film as normal. Overexposing colour negative film, especially Portra, is done regularly and its results are widely regarded as pleasant. Expect more pastel, washed out colours. Check this source for some examples of overexposed Portra.
2. Pull process the film. Push processing is the act of underexposing film, and then increasing the development time to still get proper density. In this case you overexposed the film by exposing the film as if it was less sensitive to light, so shortening the development time would here correct for the otherwise too dense film base. Pull processing will generally produce less contrast and reduced grain.

Which option you choose is up to you, but both will naturally result in different results than those you are used to when shooting Portra 400 at box speed.