For Eclipse:
FirstMethod:
| data-sap-ui-compatibilityVersion="1.28.11" |
Second method:
To install your previous version by using https://sapui5.hana.ondemand.com/1.26.1/resources/sap-ui-core.js.
Goto Help---->install new software---->enter this url.
For GUI:
Same concept, Download your previous version. Install the same in ECC system
Thanks,
KA