Thanks for a quick answer
I did it
In mainnav.php change:
<div class="navbar-header">
to
<div class="navbar-header pull-right">
and
<button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".t3-navbar-collapse">
to
<button type="button" class="navbar-toggle pull-left" data-toggle="collapse" data-target=".t3-navbar-collapse">
in off-canvas.php change:
<button class="btn btn-primary off-canvas-toggle pull-right<?php $this->_c('off-canvas') ?>.....
to
<button class="btn btn-primary off-canvas-toggle<?php $this->_c('off-canvas') ?>.....
in style.less add:
// ---------------------------------------------------------
// MAINNAV
// ---------------------------------------------------------
@media screen and (max-width: @screen-xs-max) {
#t3-mainnav .navbar-header.pull-right {
float: none !important;
}
}