When you symbolise a text box for the first time, the symbol will appear above or below it depending on what you set in the Commtap Symboliser preferences.
To change this setting, first open "preferences" from the Commtap Symboliser group in the ribbon:
Choose either "Text below symbol", or "Text above symbol", then choose "Save".
This will change the setting for when text boxes are symbolised for the first time - it has no effect on text boxes you have already symbolised.
If you select "Set as default for new documents", this setting will be used when you create a new PowerPoint document.
Moving the text box/picture/symbol around
Once you have symbolised a text box, you can still move it or the picture/symbol anywhere on the page - and if you were to symbolise the text box again, the corresponding picture/symbol will still change as appropriate.