We are trying to resize our logo for the header, but it won’t resize into the recommended 350×70 px. The current size of the original .png is 960×720 px. Do we need to resize and keep it as a .png file in Ps, or how should we resize it?
your logo doesn’t have to ‘fit’ the recommended size – once the Logo is added you can resize it in Customizer > Site Identity with the Logo Width option.