Just follow this advice:

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

This message tells you what you can and need to do in order to get your question reopened:

1. You should get the Tour to make yourself familiar with the site's format.
2. You should read How do I ask a good question? to make sure you make your question a valuable one.
3. Search, and research
   In your case it would be helpful to search for the main error message – AppStream cache update failed – on AU as well as the internet in general. Try to get to the bottom of the problem and include the whole result of your research in your question. Please do not use comments to add information, instead edit the question directly.
4. Be on-topic ✓
5. Be specific
   If you find other resources which cover your problem (like Unable to 'apt-get dist-upgrade' due to appstreamcli database error in your case) and they don't solve your problem, include them and explain how exactly the solutions proposed there don't work for you. Show us what you tried.
6. Make it relevant to others ✓
7. Keep an open mind
   Believe it or not, but we're really trying hard to help you here – we just need you to help us help you.

Just follow this advice:

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

This message tells you what you can and need to do in order to get your question reopened:

1. You should take the Tour to make yourself familiar with the site.
2. You should read How do I ask a good question? to make sure you make your question a valuable one.
3. Search, and research
   In your case it would be helpful to search for the main error message – AppStream cache update failed – on AU as well as the internet in general. Try to get to the bottom of the problem and include the whole result of your research in your question. Please do not use comments to add information, instead edit the question directly.
4. Be on-topic ✓
5. Be specific
   If you find other resources which cover your problem (like Unable to 'apt-get dist-upgrade' due to appstreamcli database error in your case) and they don't solve your problem, include them and explain how exactly the solutions proposed there don't work for you. Show us what you tried.
6. Make it relevant to others ✓
7. Keep an open mind
   Believe it or not, but we're really trying hard to help you here – we just need you to help us help you.