In this tutorial, I will explain how to place 300x250 ad banner under header of Blogger mobile view. The banner can be Google adsense ad, an affiliate program banner or a personal advert banner to promote your products and services. So, I expect you have saved the code for the banner somewhere. You can increase your Adsense earnings by placing a 300x250 ad banner under your blog header section as explained in this post.
To get started, sign in to your Blogger account via www.blogger.com ==> Go to your blog dashboard,click on "Template". ==> Click the settings icon under "Mobile", Select "Yes.............", choose "Custom" and Save. ==> Go back to "Template" > "Edit HTML" ==>Use CTRL F to find id='main' in the HTML ==> Edit showaddelement to yes and add maxwidgets='3' so it becomes similar to the code below:
==> Click "Save Template". ==> Go to "Layout' and you should now be able to add a gadget above the post area as seen in screenshot below.
==> Click the "add a gadget", select "HTML/Javascript" ==> Copy and paste your ad code in it and save. ==> Click the "edit" link next to the gadget ==> Click in the address bar of the gadget window and scroll to the end of the address as seen in the screenshot below: 
Take note of the gadget id and close the window. In the screenshot above, the id is HTML1 ==> Go to "Template" > "Edit HTML" ==> Use CTRL F to find the gadget id in your template ==> Add mobile='yes' to it so it becomes similar to the code below ==> Click "Save Template" ==> Use CTRL F to find ]]> ==> Paste the code below, directly above the ]]> #HTML1{ display : none; } @media all and (max-width: 768px) { #HTML1{ display : block; } } Replace the gadget id with yours. Click 'Save Template" View your blog on mobile phone and you should see the banner displayed under the header. I hope this works for you. NB: If you set it to mobile='only', it will be giving you errors while saving arrangements in the layout section. If you need help placing Google ads on your blog, contact me. I will only charge you a token.
To get started, sign in to your Blogger account via www.blogger.com ==> Go to your blog dashboard,click on "Template". ==> Click the settings icon under "Mobile", Select "Yes.............", choose "Custom" and Save. ==> Go back to "Template" > "Edit HTML" ==>Use CTRL F to find id='main' in the HTML ==> Edit showaddelement to yes and add maxwidgets='3' so it becomes similar to the code below: 
==> Click the "add a gadget", select "HTML/Javascript" ==> Copy and paste your ad code in it and save. ==> Click the "edit" link next to the gadget ==> Click in the address bar of the gadget window and scroll to the end of the address as seen in the screenshot below: 
Take note of the gadget id and close the window. In the screenshot above, the id is HTML1 ==> Go to "Template" > "Edit HTML" ==> Use CTRL F to find the gadget id in your template ==> Add mobile='yes' to it so it becomes similar to the code below 