It seems that with position:absolute in use an element cannot be centred using justifyContent or alignItems. There's a workaround to use marginLeft but does not display the same for all devices even using dimensions to detect height and width of device.
bottom: { position: 'absolute', justifyContent: 'center', alignItems: 'center', top: height*0.93, marginLeft: width*0.18, }, bottomNav: { flexDirection: 'row', },