What error do you get?

Parse error: syntax error, unexpected T_STRING, expecting ';' in /mnt/web-data1/???/public_html/www/administrator/components/com_booking/helpers/html.php on line 637

That method works for me.

Did you replace old method? And do you have all characters from posted code?

What row do you have on line 637? And what row is before it? (don't need empty rows but row, where is part of code). Is line before 637 finished with character ';'?

I replace method getMonthsSelect()

on line 637 i have

for ($i = 0; $i toFormat('%m') . ',' . (int) $date->toFormat('%Y')), ($date->toFormat('%B') . '/' . $date->toFormat('%Y')));

my html.php is in attachments

You had more bugs there. Function getWeekSelect was probably modified too. Both functions repaired.