1- Go to your hosting file manager or ftp and find wp-content/themes/sweetdate and copy the file header.php to your computer
2- Go to wp-content/themes/sweetdate-child and paste the header.php file there
3- Edit the header.php and find
COPY CODE
<li class="header-login-button"><a href="#" class="tiny secondary button radius"><i class="icon-user hide-for-medium-down"></i>
</a></li>
Replace with
COPY CODE
<li class="header-login-button"><a href="YOUR NEW LOGIN URL HERE" class="tiny secondary button radius"><i class="icon-user hide-for-medium-down"></i>
</a></li>
Find
COPY CODE
<li class="header-register-button"><a href="#" class="tiny button radius"><i class="icon-group hide-for-medium-down"></i>
</a></li>
Replace with
COPY CODE
<li class="header-register-button"><a href="YOUR NEW REGISTER URL HERE" class="tiny button radius"><i class="icon-group hide-for-medium-down"></i>
</a></li>